UREA 



39 



To Suction 



nation of urea in urine, blood, etc., was first proposed by Marshall, 

 whose methods have been modified by Van Slyke and Cullen. 

 These latter investigators prepared a permanent preparation of 

 the enzyme, in a water-soluble form, the use of which makes 

 more convenient the rapid and accurate determination of urea 

 in urine, blood and other biological fluids. 



The urease method is probably the most satisfactory of all 

 methods for the determination of urea. Other nitrogenous con- 

 stituents such as allantoin are not decomposed by urease. The 

 method involves no carefully regulated heating procedures, and 

 is applicable to diabetic urines. 



The procedure for the determination in urine consists in treat- 

 ing the urine sample with urease, adding an alkali and aerating 

 the liberated ammonia 

 into fiftieth-normal acid, 

 and titrating the excess 

 of acid with fiftieth- 

 normal alkali. 



Procedure of Van 

 Slyke and Cullen. 1 

 Dilute 5 c.c. of urine 

 to 50 c.c. with ammonia- 

 free water. Measure 5 

 c.c. of the diluted urine 

 into Tube " A " of the 

 Van Slyke and Cullen 

 apparatus (Fig. 1) add 

 1 drop of caprylic alco- 

 hol (to prevent froth- 

 ing), and 1 c.c. of enzyme 

 solution. Close " A " 

 with stopper and let 

 the tube stand fifteen 

 minutes for the enzyme 

 to act. Measure into 



Wash Bottle' 



FIG. 1. Van Slyke and Cullen Apparatus. 



Tube " B " 25 c.c. of N/50 HC1 or H 2 SO 4 . Add 1 drop of 

 caprylic alcohol and 1 drop of a 1 per cent alizarin solution, 

 as indicator. Connect Tubes " A " and " B " so that the 

 current of air passes from the urine to the acid. Let the air be 

 1 Van Slyke and Cullen: Jour. Biol. Chem., 1914, 19, 211. 



